1. Field of the Invention
This invention relates to gas chromatograph systems.
2. Background Art
It is known in the art to flow a carrier gas from a source through tubing to carry a sample to be analyzed into a gas chromatographic system. The carrier gas carries the sample from an injector where it has been volatilized into an analytical column. The column effluent then flows to a thermal conductivity detector for subsequent analysis. The effluent from the thermal conductivity detector may then be separated and the separated portions of the effluent may be directed to a waste trap or to one of a plurality of collection traps.
However, conventional preparative-scale gas chromatographic systems have had difficulties in functioning adequately with chemicals having very low volatilities such as alkyl toluenediamines. Such chemicals may be solid at room temperature and are particularly difficult to isolate from process reaction mixtures in sufficient quantities and purities for molecular characterization. These compounds have tended to solidify and block valves and conduits throughout the gas chromatographic system with a hard, viscous condensate. They have also exhibited very aggressive characteristics towards the materials and elements of the system.
Inadequate vaporization of these low volatility components in the injector has caused samples to remain in the injector port and subsequently clog the injector. In addition, low volatility has also resulted in insufficient sample material being introduced into the column. It was also observed that unacceptable carry-over was experienced from one injection to the next.
Additionally, very low collection efficiency of the isolated components was observed. The design of the collection system encouraged aerosoling of separated components and subsequent loss to the environment. Low volatility components are particularly susceptible to this aerosoling phenomenon.
In addition to blockage of injector ports, blocking of the conduits and valves within the collection and separation system was a serious problem. Prior systems provided a conduit with a flow of carrier gas connected to this system to flush and clean the system. Thus, the carrier gas could be directed through the valves and conduits of the separation and collection system for cleaning. However, when low volatility compounds such as alkyl toluenediamines solidify and deposit hard, viscous condensate within the conduits and the valves, the carrier gas could not remove them. Thus the collection and separation systems had to be frequently dismantled to be cleaned in order to prevent the residue of previous analytes from interfering with later results.
Another area of difficulty for very low volatility compounds was observed at the outlet of the thermal conductivity detector of gas chromatographic systems. A conduit was provided for the flow of effluent from the outlet of the thermal conductivity detector to the separation and collection system. However, the connection between the conduit and the thermal conductivity detector outlet was a source of heat loss leading to a "cold spot." Low volatility compounds had a tendency to condense at the "cold spot."
When these materials finally passed through the system to condensation tubes there was excessive aerosoling in the tubes as previously described. This lead to inefficient condensation and collection of sample components which was particularly undesirable in isolating components that are only available in extremely low concentrations. It has been known in the art to block the end of the condensation tube with a quantity of glass wool to decrease aerosoling. While this helped with the aerosoling problem, a portion of the separated material which was being collected would condense on the glass wool. This further contributed to a decrease in collection efficiency since material condensed on the glass wool rather than on the condensing tube could not be easily recovered. In addition, the presence of the glass wool could lead to blockage of the condensation tube when sufficient material condensed on the glass wool.